This invention relates generally to injection molding machines and more particularly to injection molding machines having vertically oriented clamp systems.
xe2x80x9cVerticalxe2x80x9d injection molding machines consist of an injection unit mounted either with a horizontal or vertical orientation and a clamp system oriented vertically to hold the two mold halves together under force sufficient to resist the pressure exerted by the molten plastic. Orientation of the clamp system vertically allows for operational ease as compared with horizontal clamp systems for certain applications including, but not limited to, insert molding and cable connectors.
The clamp systems commercially used in today""s vertical injection molding machine generally comprise either a three platen (or plate) or xe2x80x9cCxe2x80x9d-frame systems.
Tie bar type machines typically use three main plates conventionally known as a stationary platen, an end platen, and a movable platen. In these designs, the stationary platen mounts the stationary mold half and the movable platen mounts the movable mold half. The end platen is used to mount the traverse actuators and the tonnage actuators. In a straight hydraulic clamp, the end platen houses the tonnage cylinder. In a toggle clamp, the end platen mounts the tonnage cylinder and the toggle linkage mechanism employed as a force multiplier. In either system, the end platen is used to react the forces when tonnage is developed to hold the two mold halves together. This is a general description of tie-bar or tie rod type machines present in the commercial marketplace. Within the patent literature, a number of variations are present.
In C-frame machines there are no tie bars and a large frame acts as both the stationary platen and the end platen. The stationary half of the mold mounts to the lower C-frame and the movable mold half mounts to the movable platen. The movable platen is again driven by actuators mounted on the upper C-frame and may be either straight hydraulic or incorporate a toggle linkage to develop tonnage. In either system, the C-frame upper and lower halves act to react against the force generated during tonnage application. This is a general description of C-frames in the commercial marketplace today. Within the patent literature, variations probably exist.
The overall height of the conventional vertical machines is therefore higher than what is otherwise required because of the presence of the end plate or the top leg of the xe2x80x9cCxe2x80x9d-frame. It is to be appreciated that, because the stationary platen of a vertical injection machine is mounted to ground, vertical molding machines are inherently suited to large, heavy mold applications requiring high mold tonnage. Conventional, large vertical machines thus require massive mold frames which raise height clearance concerns. In contrast, horizontal machines have length concerns but such concerns can be addressed, in most instances, by plant layout techniques.
More recently, the injection molding machine industry has begun commercializing two-platen mold clamping systems which have reduced the length of horizontal machines. Reference can be had to assignee""s U.S. Pat. No. 5,776,516 to Armbruster et al., issued Jul. 7, 1998, for an example of a two-platen mold assembly.
In the patent literature, reference can be had to U.S. Pat. No. 5,338,171 to Hayakawa et al., issued Aug. 16, 1994, for a description of a number of mold clamp systems, including a two-platen system for a vertical machine. The two-platen mold systems under discussion are characterized by high tonnage, hydraulic piston-cylinder units with small piston travel displacing little hydraulic fluid because a smaller driving cylinder, pneumatic or hydraulic, is used to move the mold halves into and out of molding engagement. The movable platen moves into and out of molding engagement and is maintained in molding engagement under high tonnage by tie rods or by bushings for guide bars and the like. For the horizontal machine, this mounting/guiding arrangement is acceptable because the weight of the platen can be supported by rollers (indirectly in contact with ground) which can also assure alignment. For the vertical machine, the guide bars must closely control and guide the movable platen to assure consistently repeatable cycles necessary for the mold guide pins to properly align the mold halves. Bushings wear and require constant maintenance to assure lubrication of clean surfaces.
Additionally, the high tonnage lock rods must be positively locked for clamp tonnage and unlocked. Also, there are safety requirements that require the mold position to be locked in event of power failure, emergency stop, intrusion into the clamp zone, etc. The requirements are especially pertinent for vertical injection molding machines because they require that the movable platen be prevented from dropping vertically. Typically, the safety requirements for a positional lock are met by a locking rod which is usually located out of the center of acting forces. In the case of an emergency lock, a conventional locking rod could create significant damage to the system because of disproportional distribution of inertia forces. In one of the inventors"" earlier patents, U.S. Pat. No. 5,035,606, issued Jul. 30, 1991, a fail safe locking arrangement is disclosed which overcomes many of the problems present in conventional locking arrangements. This invention improves on the locking arrangement disclosed in the ""606 patent which is incorporated herein by reference.
A particular advantage that vertical injection molding machines possess is the ability for the machines to be equipped with a rotating table overlying the stationary platen. The table is equipped with a plurality of stationary mold halves that are rotated by the table through successive work stations to reduce the overall process time. For example, after molding, the stationary mold half with the molded part is rotated to an ejector station where ejector pins dislodge the molded part from the mold cavity. The transfer to an ejection station while another mold half is simultaneously rotated into a molding relationship with the movable platen, reduces the cycle time otherwise required in a horizontal machine to eject the part, or alternatively, employ complicated mold transfer mechanisms to shuttle mold halves into and out of the clamp. Other stations on the rotating table may be dedicated to robotic part removal, insert placing, etc.
Typically, the table is rotated in sliding contact with the stationary platen and the station position is determined by limit or proximity switches. The sliding table motion requires lubrication and maintenance and also limits the mold weight of a machine otherwise inherently suited for executing large clamping forces.
Accordingly, it is a general object of the present invention to provide an improved vertical type injection molding machine which addresses the concerns discussed in the Background.
This general object along with other features of the invention is achieved in a vertical injection molding machine which includes a lower stationary platen upon which a lower mold half is mounted and an upper vertically movable platen on the bottom side of which is mounted an upper mold half in confronting relation to the lower mold half. An advance mechanism is provided for raising and lowering the movable platen relative to the stationary platen and the machine has an injection unit for injecting molding material into one of the mold halves when the mold halves have been moved into a molding relationship. A plurality of vertically extending locking rods positioned to straddle the mold halves is provided with each locking rod being attached at one end thereof to the stationary platen (for example, by being connected to a high tonnage clamp piston of a cylinder mounted to the stationary platen). Each locking rod extends through a locking rod opening in the movable platen and has a plurality of longitudinally spaced annular grooves extending over a rod length adjacent the opposite locking rod end (i.e., the top end) to a position which is at least adjacent to the movable platen. A locking device is provided on the top side of the upper movable platen for locking the upper movable platen at any set distance from the stationary lower platen.
The locking device includes a caliper for each locking rod having inboard and outboard caliper halves with each caliper half having a generally semi-circular, radially inward protruding lock ring adapted to fit within a locking groove when the inboard and outboard caliper halves are moved together to form a generally circular locking ring. The locking device further includes first and second actuating rods. The first rod is secured to the inboard caliper half of a first caliper at one end of the rod and to the outboard caliper half of the second caliper at the opposite end of the first rod. Similarly, the second actuating rod is secured to the outboard caliper half of the second caliper at one end of the second rod and to the inboard caliper half of the first caliper at its opposite end. The locking device also includes a piston rod connector plate and a cylinder connector plate. The piston rod plate is secured to the first actuating rod at a first distance between the ends of the rod and through which the first actuating rod extends and, in addition, has a first opening for slidably receiving the second actuating rod. Similarly, the cylinder connector plate is fixed to the second actuating rod at a second distance between the ends of the second actuating rod and through which the rod extends and also has an opening for slidably receiving the first actuating rod. A compression spring is situated between the piston rod connector plate and the cylinder connector plate to simultaneously bias both inboard and outboard caliper halves of both first and second calipers to a closed position while an opening mechanism also attached to the piston rod connector plate and the cylinder connector plate is provided for drawing the connector plates towards one another to simultaneously open both inboard and outboard caliper halves of both first and second calipers. Thus, the locking mechanism provides an always on, spring biased locking device simultaneously locking two calipers and their associated locking rods to meet safety concerns while a power-on arrangement is utilized to disable the locking device for raising and lowering the upper movable platen at the completion and commencement of successive molding cycles.
In accordance with another aspect of the invention related to the locking device, the movable platen is generally rectangular in configuration having longitudinally extending sides and short sides with a locking device adjacent a long side on the top surface of the movable platen so that the machine has two locking devices and the first and second calipers of each locking device assembly are positioned at opposite corners of a long side so that each machine has four locking rods. The opening mechanism includes a piston movable within a cylinder housing mounted to the cylinder connector plate and the piston has a piston rod extending therefrom mounted to the piston rod connector plate. Additionally, the cylinder housing has a cylinder stop rod protruding in an opposite direction from the piston rod. A piston rod mounting block is provided which is secured to the movable platen and through which the piston rod slidably extends and also a cylinder rod mounting block is provided which is, likewise, secured to the movable platen and through which the cylinder rod slidably extends. The actuating rods are connected only to the caliper halves and to the connector plates and the connector plates, in turn, are only connected to the piston/cylinder opening mechanism which, in turn, is connected to the movable platen only by the sliding fit established by the mounting blocks so that the locking device is free to float allowing the actuating rods to center themselves in the calipers to assure positive opening and closing of the locking device.
In accordance with a more specific feature of the invention, the floating arrangement of the actuator rods is continued into the design of the calipers which includes a caliper block secured to the movable platen adjacent a long side of each caliper and functioning as the only attachment of the caliper to the movable platen. The caliper (or alternatively, the caliper mount) has a longitudinally extending groove and the caliper mount (alternatively, the caliper) has a protrusion slidable in the groove duplicating the sliding attachment provided for the piston/cylinder opening mechanism of the locking device. A lubricated wear plate between caliper halves and the moving platen assures movement of the caliper halves. The caliper mounting arrangement further assures full utilization of the compressive force of the locking device spring without sticking or binding of the device thus avoiding more complicated caliper tie-down arrangements such as the utilization of a top plate and/or the requirement of having multiple lock rings in each caliper.
In accordance with another aspect of the invention that further assures positive actuation of the locking devices, each caliper has a long side generally parallel to the long side of the movable platen. Any given caliper has an actuating rod secured to an outboard caliper half and an actuating rod secured to an inboard caliper half adjacent one long caliper side while an actuating rod secured to an inboard caliper half and an actuating rod secured to an outboard caliper half is adjacent to the opposite long caliper side so that even clamping forces are distributed by four actuating rods to each caliper. Thus, each machine has two locking devices. Each locking device locks and unlocks two locking rods and each locking device has four actuating rods.
In accordance with another aspect of the invention, the opposite or top locking rod ends of each locking rod are secured to a locking rod bridge. A proximity (or alternatively a limit) switch on a caliper senses the position of the teeth and grooves on one of the locking rods. The advance mechanism lowers the movable platen to a molding position whereat the short stroke, high tonnage piston/cylinders can exert a clamping force on the mold halves. The locking rod bridge assures that all four corner positioned locking rod teeth and grooves are in reasonable alignment at the molding position so that the locking ring of each caliper can fully engage a groove/shoulder in the locking rod when the advance mechanism brings the mold halves into molding relation prior to actuation of the high tonnage actuators. In the preferred embodiment, the locking rod bridge is a simple structural steel fabrication, preferably of angle iron which has good resistance to twisting while lacking any significant load bearing capacity (since that function is performed by the calipers and locking rods in the upper platen). Locking rod alignment of all four locking rods as a unit is therefore maintained by a special mounting arrangement firmly securing the bottom end of each locking rod to the piston of a high tonnage piston/cylinder that allows a floating connection when the movable platen is raised or lowered while the opposite top end of all locking rods are tied together by the locking rod bridge.
In accordance with another somewhat separate but related aspect of the invention, a vertically extending ladder frame is mounted to the stationary platen. The vertical ladder frame has a pair of laterally spaced and parallel vertical guide rails which are secured to the frame and each guide rail has a pair of runner blocks slidable on the rails in a secure manner. A pair of parallel mounting block plates are secured to one of the long sides of the movable platen and extends above the top surface and below the bottom surface of the movable platen. Each mounting block plate confronts a guide rail and the runner blocks are secured to the block mounting plates above and below the top and bottom movable platen surfaces so that the movable platen is maintained and aligned at a set relationship to the stationary platen throughout its travel. This arrangement obviates the need for close toleranced bushings and sleeves to be fitted within the movable platen which would otherwise be required to maintain alignment (within thousandths of an inch to assure seating of guide pins, sleeves, etc.) of the confronting mold halves.
In accordance with another specific aspect of the invention, the vertical frame also mounts one end of each of the carriage positioning/reaction cylinders of the injection unit to a reaction block slidable on a vertical support, in turn, fixed at each end thereof to a cross-over member on the vertical frame. The nozzle of the injection unit extends between the vertical supports and the carriage positioning/reaction cylinders mounted to the injection unit are free to vertically move and maintain alignment as the injection unit is raised or lowered by a lift mechanism to proper molding height.
In accordance with another somewhat separate but related feature of the invention, the vertical injection molding machine is equipped with a generally circular table which rests on the stationary platen during molding. The table has a central opening. A multi-purpose spindle journaled in a spindle mounting block, in turn, mounted to the stationary platen extends through and is secured to the central opening to allow table rotation about the spindle. A lift mechanism which includes a pair of table actuators is provided radially outward from the spindle and on diametrical opposite sides thereof. Each table actuator has at least one spherical roller that is spring biased into contact with a hardened, flat circular track plate inserted in the bottom of the table. Each roller is mounted in a spring biased roller block which, in turn, is mounted in a vertically movable manner to a lift actuator block mounted to stationary platen and containing a power actuator for raising the roller mounting block. The rollers lift the table when the actuators are in an actuated position and roll on the track plate as the table is rotated about the spindle by a motor driven pinion gear meshing with a ring gear extending about the circumference of the table. Lifting the table for rotation avoids the sliding, lubricated arrangement otherwise used, thus reducing the power requirement to rotate the table and allowing heavier bottom mold halves (for increased molding tonnage) to be mounted on the table. When the table has rotated a bottom mold half to its molding station and is lowered to rest on the stationary platen, the springs in the roller block maintain the rollers in contact with the track plate to avoid roller/track damage resulting from impact which could otherwise occur when the table actuators subsequently push the table upward on the rollers.
In accordance with another aspect of the rotary table, the rotating spindle is not only hollow to permit liquid connections (for mold temperature control) to be made with the spindle to work stations on the top surface of the table, but also a plurality of hydraulic actuator connections are provided through the spindle. Within the spindle mounting block are a plurality of vertically spaced hydraulic inlet lines and a like plurality of vertically spaced hydraulic return lines, each line taking the form of a ring groove in the spindle mounting block. Each inlet line communicates with a circumferential inlet spindle groove leading to a vertically extending inlet passage formed in the wall of the hollow spindle exiting at the top surface of the table. Each return line similarly communicates with a circumferential return spindle groove leading to a vertically extending return passage formed in the wall of the hollow spindle exiting at the top surface of the table. The spindle grooves have flared openings spanning a vertical distance at least equal to the table lift travel which always remain in fluid communication with spindle mounting ring grooves. O-ring or elastomer seals between and vertically spaced from spindle grooves and spindle mounting block ring grooves prevent leakage during spindle rotation and vertical movement thereby allowing hydraulic cylinders mounted at work stations on the top of the table to be connected to the machine""s hydraulic pumps with pressure controlled by the machine""s programmable controller.
In general summary, the invention resides in the provision of an improved vertical injection molding machine which has the following features either alone or in combination with one another:
a) An improved lock for the movable platen having among its distinguishing features i) an always on lock for each locking rod meeting safety requirements, ii) simultaneous operation by one locking device (two locking devices per machine) for simultaneous clamping and unclamping of two locking rods, iii) floating structure allowing centering and full utilization of the spring clamping forces by four actuating rods for each locking device; and/or, iv) floating alignment bridge for locking rods to assure locking device engagement;
b) A vertical frame to i) keep low machine height for two-platen machines, ii) stably support movable platen throughout vertical travel without the need of close tolerance tubes or bushing, and/or iii) provide a convenient mount for carriage, position/reaction cylinders of injection unit;
c) A rotatable lift table to i) allow operation with heavy mold sets to utilize inherent advantages of a vertical clamp machine, ii) reduce power otherwise required to rotate table, and/or iii) provide hydraulic actuator and/or liquid connections at table center.
These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the Detailed Description of the Invention set forth below taken in conjunction with the drawings.